1. Field of the Invention
The present invention relates to a photo sensor. More particularly, the present invention relates to a photo sensor of a portable electronic apparatus.
2. Description of Related Art
FIG. 1 is a cross-sectional view of a conventional photo sensor. Referring to FIG. 1, the conventional photo sensor 100 includes a substrate 101, a metal electrode 102, a semiconductor layer 104, a doped semiconductor layer 106 and a transparent electrode 108. Wherein, the metal electrode 102 is disposed on the substrate 101. Moreover, the semiconductor layer 104 and the doped semiconductor layer 106 are disposed between the metal electrode 102 and the transparent electrode 108. Material of the transparent electrode 108 can be indium tin oxide (ITO). The doped semiconductor layer 106 can be used for reducing impedance between the transparent electrode 108 and the semiconductor layer 104.
To be specific, the metal electrode 102 can be electrically connected to a low voltage, and the transparent electrode 108 can be electrically connected to a high voltage. Since the semiconductor layer 104 is formed by a photosensitive material, when an external light L passes through the transparent electrode 108 and irradiates the semiconductor layer 104 and the doped semiconductor layer 106, the semiconductor layer 104 absorbs photons to generate electron-hole pairs. The electrons and the holes respectively flow and migrate to the transparent electrode 108 and the metal electrode 102 during existing times thereof to form a photocurrent.
It should be noted that a fabrication process of the conventional photo sensor 100 cannot be integrated with a standard 5-mask process for fabricating an active device array substrate. This is because during the standard 5-mask fabrication process, a source/drain metal layer serves as a mask for fabricating an ohmic contact layer (doped semiconductor layer). In other words, during the standard 5-mask fabrication process, the Ohmic contact layer (doped semiconductor layer) cannot be successfully fabricated without the source/drain metal layer. However, in the conventional photo sensor 100, the transparent electrode 108 is located above the doped semiconductor layer 106, so that the doped semiconductor layer 106 cannot be formed during the standard 5-mask fabrication process. Moreover, the photo sensor 100 without the doped semiconductor layer 106 can be malfunctioned due to an excessive impedance. Therefore, how to integrate the photo sensor 100 onto the LCD panel is an essential subject to be developed.